The invention relates to the design and process for making cementitious grouts. More specifically, the invention relates to compositions and methods for making self-consolidating grouts containing fly ash and ground granulated blast furnace slag.
Grout is a cementitious material used to fill voids and volumes in the construction of masonry structures. It differs from concrete mixtures in that the aggregates are considerably finer in particle size which allows it to flow into finer passages such as, for example, the internal volumes of a typical 8″×8″×16″ concrete masonry block (CMU). Grout mixtures can be divided in two basic functional groups; conventional (non-consolidating) grout and self-consolidating grout.
Conventional (non-consolidating) grout has been the default material used for many years. It has a relatively high viscosity (compared to self consolidating types), characterized by “slump” measurements of between 8″ and 11″, per ASTM C 476. Slump is measured by filling an inverted hollow cone with grout, then pulling the cone, allowing the grout mixture to “fall”, creating a collapsed mass. The difference in height between the original cone height and the top of the collapsed mass of grout is the “slump”. Compared to concrete, conventional grout has a higher (falls more) slump because it must flow into passages and around objects (like reinforcing bar) that concrete cannot. However, to insure complete penetration of grout into passages and around objects, and to minimize voids, conventional grouts must have mechanical vibration applied during filling. This can be time consuming and expensive. Due to the limited flow-ability of conventional grout, the maximum length of any given fill is limited, so grout filling must be accomplished in stages with vibration applied in each stage.
Conventional non-consolidating grout is typically comprised of Portland cement or cement mixtures and an aggregate. Aggregates typically comprise sand or sand and pea gravel mixtures, in accordance with ASTM C 476. Chemical “admixtures” may be added to modify properties. Since Portland cement is energy intensive to manufacture and somewhat expensive, there has been an effort by researchers to substitute components like fly ash and blast furnace slag for a portion of the cement. Typically, however, these materials reduce the compressive strength of the grout, or extend the time period it takes to achieve the minimum strength of 2000 psi specified by ASTM C 476.
Self-consolidating grouts are more recent mixtures having better flow characteristics than conventional non-consolidating grout. Typically, they do not require vibration to flow into passages, around re-bar and have reduced void formation. Due to the reduced effective viscosity of self-consolidating grouts, their flow properties are not measured by conventional “slump” testing, as described above. Instead, “slump flow” is used, which is the diameter of a reference sample volume after being poured onto a flat surface. The larger the diameter, the more fluid the sample is and the greater the “slump flow”. Due to the increased fluidity, there is concern about segregation of the components and aggregate, which is undesirable. So, these grouts contain various chemical compounds to suspend aggregates and other components in a uniform manner. These compounds are often referred to as “admixtures”, and typically take the form of polycarboxylates or related compounds. Polycarboxylates act as a suspending and fluidizing agents, which also reduce the amount of water required in the mixtures. To further improve flow characteristics, other viscosity modifying compounds may also be added. The potential disadvantage of these self-consolidating mixtures is cost. Although they save money during the pouring and filling stages, they still contain Portland cement for the most part, with the addition of expensive hydrocarbon based admixtures.
Recently, researchers have been reporting on the composition of self-consolidating grouts that contain significant portions of fly ash and ground granulated blast furnace slag, without the addition of admixtures. For example, Mwangi et al. reported on the performance of self consolidating grout mixtures containing fly ash and ground granulated blast furnace slag in a paper presented to the 12th Canadian Masonry Symposium, June 2013. Although the 28 day compressive strengths of the cured grout were just shy of the minimum required 2000 psi, the results showed great promise. These newer self-consolidating grouts have the potential for significant cost reduction and overall energy savings, by reducing Portland cement content and eliminating the need for hydrocarbon admixtures. They also provide a sustainability improvement by the incorporation of fly ash and blast furnace slag, materials that would have otherwise needed disposal in land fills.
These and other limitations of the prior art will become apparent to those of skill in the art upon a reading of the following descriptions and a study of the several figures of the drawing.